CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 231,005	$ 215,723
Marketable securities	605,438	610,185
Receivables, net	43,666	34,462
Inventories, net	95,380	91,196
Other current assets	23,292	31,236
Total current assets	998,781	982,802
PROPERTY AND EQUIPMENT:
Aircraft and rotable spares	7,587,004	7,527,555
Deposits on aircraft	36,625	31,625
Buildings and ground equipment	253,154	258,863
Total property and equipment, gross	7,876,783	7,818,043
Less-accumulated depreciation and amortization	(2,563,123)	(2,455,995)
Total property and equipment, net	5,313,660	5,362,048
OTHER ASSETS:
Operating lease right-of-use assets	274,025	282,362
Long-term receivables and other assets	308,219	260,410
Total other assets	582,244	542,772
Total assets	6,894,685	6,887,622
CURRENT LIABILITIES:
Current maturities of long-term debt	357,463	402,158
Accounts payable	315,238	278,677
Accrued salaries, wages and benefits	122,715	125,944
Current maturities of operating lease liabilities	82,671	82,641
Taxes other than income taxes	26,523	26,183
Other current liabilities	45,828	26,119
Total current liabilities	950,438	941,722
LONG-TERM DEBT, net of current maturities	2,748,717	2,801,538
DEFERRED INCOME TAXES PAYABLE	639,046	625,931
NONCURRENT OPERATING LEASE LIABILITIES	200,598	205,845
OTHER LONG-TERM LIABILITIES	174,365	173,041
COMMITMENTS AND CONTINGENCIES (Note 7)
STOCKHOLDERS' EQUITY:
Preferred stock, 5,000,000 shares authorized; none issued
Common stock, no par value, 120,000,000 shares authorized; 82,301,551 and 82,094,985 shares issued as of March 31, 2021 and December 31, 2020, respectively	712,324	704,675
Retained earnings	2,087,906	2,052,006
Treasury stock, at cost, 31,955,991 and 31,913,635 shares as of March 31, 2021 and December 31, 2020, respectively	(618,709)	(617,136)
Total stockholders' equity	2,181,521	2,139,545
Total liabilities and stockholders' equity	$ 6,894,685	$ 6,887,622